More then 90% of cancer lesions are epithelial in origin. Several of the most common forms of epithelial cancers such as colorectal, esophageal, bladder, cervical and oral cancers have a well defined, detectable pre-cancer stage called dysplasia. Dysplasia is characterized by sequential accumulation of mutations in defined oncogenes and tumor suppresser genes. If detected, the absolute majority of the dysplastic lesions are curable. Clinical efforts to detect and treat this pre-cancerous stage of epithelial cancer have been shown to reduce the mortality rate.
Diagnosis of epithelial dysplasia remains difficult because it typically does not form macroscopic structures such as polyps, and is usually only visible after cancer has developed. Standard methods of detecting epithelial dysplasia are based on random biopsies and pathologic examination of the stained biopsy material. However, random biopsies have high sampling error. In many cases less than 1% of the epithelial surface at risk for dysplasia can be examined.
All types of epithelial dysplasia have several common characteristics, namely enlargement of epithelial cell nuclei with an increase in the nuclear to cytoplasmic ratio, nuclear hyperchromatism, and increased number and stratification of epithelial cells. Despite these well-characterized epithelial changes, classification has been difficult as demonstrated by high inter-observer disagreement, even among experienced pathologists.
Non-invasive, in-vivo methods of detecting epithelial dysplasia provide for surveillance of epithelial surfaces, and the pathological diagnosis of pre-cancerous conditions in humans.
Optical techniques are well suited to be a substitution for random biopsies, since they are non-invasive, do not require tissue removal, and can be performed in-vivo. Moreover, they are fast (can be applied in real time), are relatively non-expensive, are able to work on microscopic scale, and thus can find very small dysplastic sites. The latter are highly likely to be missed by random biopsies.
The present invention relates to light scattering spectroscopy of polarized light to provide information about scatterers in surface layers of turbid media such as tissue. This process need not utilize fluorescence or absorption spectral features, but rather scattering properties of surface tissues such as epithelial layers. It can characterize properties of large scatterers (cell nuclei) in human epithelium and provide histological information about human tissues and diagnose dysplasia in real time in human organs in-vivo.
The idea of light scattering spectroscopy of unpolarized light to determine features of epithelial tissue has been described in U.S. Ser. No. 08/948,734 filed on Oct. 10, 1997, and in International Application No. PCT/US98/21450 filed on Oct. 9, 1998, which designated the United States, the entire contents of these applications being incorporated herein by reference. The major centers of light scattering in epithelium are cellular organelles such as mitochondria and nuclei with the refractive index higher than that of the surrounding cytoplasm. Light backscattered from surface epithelial cell nuclei has an oscillatory wavelength dependent component. The periodicity of this component increases with nuclear size, and its amplitude is related to the density of the nuclei. Thus, by analyzing the amplitude and frequency of the oscillatory component, the density and size distribution of epithelial nuclei can be determined. Normal nuclei have a characteristic diameter l=4-7 xcexcm. In contrast, dysplastic nuclei can be as large as 20 xcexcm. Nuclear size and density are important indicators of neoplastic precancerous changes in biological tissue. The ability to measure nuclear size distribution in vivo and in real time has valuable applications in clinical medicine. This enables the diagnosis of precancerous changes in various human organs such as esophagus, colon, bladder, oral cavity, cervix, etc. non-invasively and in-real-time.
Epithelium covers surfaces of organs in the human body. The thickness of epithelium ranges from 20 xcexcm (one cell layer) to a few hundred microns (multiple cell layers). Beneath epithelium there are layers of relatively acellular connective and muscular tissues. Since dysplasia is limited to the epithelium, it is important to differentiate between the signal associated with the epithelium and underlying tissues, The backscattered component which caries information about surface epithelium nuclei is present in light reflected from mucosal tissue. However, it is ordinarily very small in amplitude, and easily masked by a background signal formed by diffuse scattering from the underlying tissue. To analyze that component the background signal must be removed. One can remove the diffuse background by modeling the general spectral features of the background. However, to make the approach more useful in practical medicine, and to be able to diagnose dysplasia in vivo, in real time, and in different organs, it is necessary to develop more robust method of removing or significantly reducing the diffuse component of the scattered light.
The present invention provides a method of measuring scattering features of epithelial cells by using polarized light spectroscopy. Note that initially polarized light looses its polarization while traveling through a turbid medium (tissue is an example of turbid medium). On the other hand the light scattered backward after a single scattering preserves polarization. Thus, by removing the nonpolarized component of the scattered light, one is able to distinguish light scattered by epithelial cells. The residual spectrum can be further analyzed so that the size distribution of the nuclei and their density can be determined.
A preferred embodiment of the invention includes a fiber optic light delivery and collection system for diagnose of tissue. The fiber optic system can be housed in a probe housing proximal and distal ends where the distal end can be inserted into various lumens of the human body for in vivo measurements of tissue. Polarizers can be used on the distal ends of both delivery and collection fibers. With optical fibers tat preserve the polarization of light, the polarizers can be positioned at the proximal end of the probe. In a three fiber system, the probe can use a central delivery fiber and two off-center collection fibers that collect two different polarization components of light returning from the tissue. The polarizers can be birefringent crystalline materials such as quartz, sapphire, or calcite. The calcite must be sealed from the working environment.